Ion detector for ion beam applications

Abstract

Detection of weak ion currents scattered from a sample by an ion beam is improved by the use of a multiplier system in which a conversion electrode converts incident ions to a number of secondary electrons multiplied by a multiplication factor, the secondary electrons being attracted to an electron detector by an appropriate bias. In one version, the detector is a two stage system, in which the secondary electrons strike a scintillator that emits photons that are detected in a photon detector such as a photomultiplier or a CCD.

1. An ion beam system comprising:
 a beam generator for generating and directing a primary ion beam at a sample; 
 at least one detector for detecting secondary particles scattered from said sample by said primary ion beam; 
 a conversion electrode disposed azimuthally about said detector so as to receive ions scattered from said sample, said conversion electrode being adapted to emit more than one secondary electron for each ion striking it, the number of secondary electrons being related to the number of incident ions by a multiplication factor; in which 
 said conversion electrode is biased negative with respect to a bias of said sample and said detector is biased positive with respect to said conversion electrode, whereby a first number of ions scattered from said sample and received by said conversion electrode emits said first number multiplied by said multiplication factor of secondary electrons that are attracted to said detector. 
 
   
   
     2. A system according to  claim 1 , in which:
 said detector is disposed azimuthally about said primary beam. 
 
   
   
     3. A system according to  claim 1 , in which:
 said conversion electrode has the shape of a frustrum of a cone centered on said primary beam. 
 
   
   
     4. A system according to  claim 1 , in which:
 said detector is an electrical detector that generates an electrical signal in response to an electron striking it. 
 
   
   
     5. A system according to  claim 4 , in which:
 said detector is disposed azimuthally about said primary beam. 
 
   
   
     6. A system according to  claim 4 , in which:
 said conversion electrode has the shape of a frustrum of a cone centered on said primary beam. 
 
   
   
     7. A system according to  claim 1 , in which:
 said detector is a two stage detector comprising a scintillator material that emits photons in response to an electron striking it and a photodetector that generates an electrical signal in response to said photons. 
 
   
   
     8. A system according to  claim 7 , in which:
 said detector comprises a layer of conductive material on a front surface of said scintillator, whereby a positive bias with respect to said conversion electrode applied to said conductive material attracts said secondary electrons to said scintillator. 
 
   
   
     9. An ion beam system comprising:
 a beam generator for generating and directing a primary ion beam at a sample; 
 at least one detector for detecting secondary particles scattered from said sample by said primary ion beam; 
 a conversion electrode disposed to receive ions scattered from said sample, said conversion electrode being adapted to emit more than one secondary electron for each ion striking it, the number of secondary electrons being related to the number of incident ions by a multiplication factor; in which 
 said conversion electrode is biased negative with respect to a bias of said sample and said detector is biased positive with respect to said conversion electrode, whereby a first number of ions scattered from said sample and received by said conversion electrode emits said first number multiplied by said multiplication factor of secondary electrons that are attracted to said detector; and 
 a source of ionizing photons that are directed through a plume of secondary particles scattered from said sample, whereby at least some neutral particles in said plume of secondary particles are ionized. 
 
   
   
     10. A system according to  claim 9 , in which:
 said detector is an electrical detector that generates an electrical signal in response to an electron striking it. 
 
   
   
     11. A system according to  claim 10 , in which:
 said detector is disposed azimuthally about said primary beam and said conversion electrode is disposed azimuthally about said detector. 
 
   
   
     12. A system according to  claim 10 , in which:
 said conversion electrode has the shape of a frustrum of a cone centered on said primary beam. 
 
   
   
     13. A system according to  claim 9 , in which:
 said detector is a two stage detector comprising a scintillator material that emits photons in response to an electron striking it and a photodetector that generates an electrical signal in response to said photons. 
 
   
   
     14. A system according to  claim 13 , in which:
 said detector comprises a layer of conductive material on a front surface of said scintillator, whereby a positive bias with respect to said conversion electrode applied to said conductive material attracts said secondary electrons to said scintillator. 
 
   
   
     15. A system for detecting a beam of ions comprising:
 at least one detector for detecting electrons; 
 a conversion electrode disposed azimuthally about said detector so as to receive said beam of ions, said conversion electrode being adapted to emit more than one secondary electron for each ion striking it, the number of secondary electrons being related to the number of incident ions by a multiplication factor; in which said conversion electrode is biased to attract said beam of ions and said detector is biased positive with respect to said conversion electrode, whereby a first number of ions received by said conversion electrode emits said first number multiplied by said multiplication factor of secondary electrons that are attracted to said detector. 
 
   
   
     16. A system according to  claim 15 , in which:
 said detector is an electrical detector that generates an electrical signal in response to an electron striking it. 
 
   
   
     17. A system according to  claim 15 , in which:
 said detector is a two stage detector comprising a scintillator material that emits photons in response to an electron striking it and a photodetector that generates an electrical signal in response to said photons. 
 
   
   
     18. A system according to  claim 15 , in which:
 said detector is a two stage detector comprising a scintillator material that emits photons in response to an electron striking it and a photodetector that generates an electrical signal in response to said photons. 
 
   
   
     19. A system according to  claim 15 , in which:
 said detector is disposed azimuthally about said primary beam. 
 
   
   
     20. A system according to  claim 15 , in which:
 said conversion electrode has the shape of a frustrum of a cone centered on said primary beam.